A typical measurement device designed to analyze tri-state logic systems which includes a low impedance probe (i.e., the probe is low impedance at all frequencies) will cause a floating data bus to be "tri-stated" when the probe is attached to the bus. That is, high speed, low impedance (.about.50 ohm) bus structures may tri-state to high impedances when a drive stops driving the bus. The low impedance probe may pull down the line depending on the value of the pull up resistors.